: Specific Aim 1 will examine the electrophysiological basis of calcium oscillations in GnRH neurons, the effects of specific neurotransmitters on intracellular calcium and GnRH release, and the signaling pathways mediating these effects, and test the hypothesis that the synchronization of these calcium oscillations, which occur every 50 minutes, underlies the episodic secretion of GnRH. Specific Aims 2 and 3 focus on the positive feedback actions of estradiol, using in vivo and in vitro approaches, respectively. The possible role of increased NPY and glutamate release and decreased GABA secretion in the initiation of the GnRH surge will be examined in vivo by determining the effects of estrogen treatment on levels of these neurotransmitters in the median eminence. The studies in Specific Aim 3 will test the hypothesis that estrogen acts directly on GnRH neurons in vitro to stimulate calcium oscillations and GnRH release or to alter their responsiveness to NPY, glutamate, or GABA.